Let's say you have an array like this:
//Input
[1,2,3,4,5,6,7]
How to write the function which will get us the output of
//Output
Array1 = [1]
Array2 = [1,2]
Array3 = [1,2,3]
Array4 = [1,2,3,4]
Array5 = [1,2,3,4,5]
And
//Output
1. [1,1,2,1,2,3,1,2,3,4...]
// tried this
for (i = 0; i < arr.length; i++) {
arr = new Array(arr[i]);
}
You can use functions like Array#map and Array#slice to easily create the first function, and use Array#concat with spread syntax to flatten a 2D array.
function prefixes(array) {
return array.map((_, index) => array.slice(0, index + 1));
}
function flatten(array) {
return [].concat(...array);
}
const output = prefixes([1,2,3,4,5,6,7]);
console.log(output);
console.log(flatten(output));You could reduce the array by slicing the wanted part with spread syntax ....
var array = [1, 2, 3, 4, 5, 6, 7],
result = array.reduce((r, _, i, a) => [...r, ...a.slice(0, i + 1)], []);
console.log(result);.as-console-wrapper { max-height: 100% !important; top: 0; }Use forEach and for loop
var arr = [1, 2, 3, 4, 5, 6, 7];
var arrys = [];
//lopping over the array, and creating the new array and putting values
// equal to number of index
arr.forEach(function(item, index) {
var tempArray = [];
for (var m = 0; m <= index; m++) {
tempArray.push(arr[m])
}
arrys.push(tempArray)
})
console.log(arrys)
// flat the previously created array
var flatten = [];
arrys.forEach(function(item) {
item.forEach(function(item2) {
flatten.push(item2)
})
})
console.log(flatten)You can do this simply by using two nested for loops like this,
let arr = [1, 2, 3, 4, 5, 6, 7];
function foo(arr) {
let rarr = [];//result array
for (let i = 0; i < arr.length; i++) {
let a = [];//array[i]
for (let j = 0; j <= i; j++) {
a.push(arr[j]);
}
rarr.push(a);
}
return rarr;
}
console.log(foo(arr));
**********?